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Ding H.,Tsinghua University | Song Y.,Tsinghua University | Hu Z.,Tsinghua University | Wu J.,China Longyuan Power Group | Fan X.,China Longyuan Power Group
Zhongguo Dianji Gongcheng Xuebao/Proceedings of the Chinese Society of Electrical Engineering | Year: 2013

Distribution of wind power forecast error significantly affects the decision of dispatch and reserve etc. in power systems. Based on the 'wind to power' day-ahead forecast procedure of wind farms, this paper put forward an approach to determine the probability density function of day-ahead wind power forecast error of wind farms. Firstly, this paper studied the power curve of wind power with least square fitting method and analyzed the influences of power curve-fitting error on day-ahead wind power forecast. Then the fitted power curve was used to study how the wind speed forecast error affects the wind power forecast error in different speed intervals analytically and by simulation. Finally, Monte-Carlo two-stage sampling was used to simulate the common effect of the fitting error of power curve and wind speed forecast error. The distributions of day-ahead forecast errors corresponding to different speed intervals were determined with Maximum Likelihood Estimation. Case study results based on historical data of an actual wind farm show that the proposed method can precisely depict the wind power forecast error under different wind speed, determine the proper wind speed range for each probability distribution, and provide references for optimal dispatch. © 2013 Chin. Soc. for Elec. Eng.

Jia S.,Tsinghua University | Wang X.-S.,Tsinghua University | Ren H.-H.,Tsinghua University | Ren H.-H.,China Longyuan Power Group
Chinese Physics B | Year: 2012

High density packaging is developing toward miniaturization and integration, which causes many difficulties in designing, manufacturing, and reliability testing. Package-on-Package (PoP) is a promising three-dimensional high-density packaging method that integrates a chip scale package (CSP) in the top package and a fine-pitch ball grid array (FBGA) in the bottom package. In this paper, in-situ scanning electron microscopy (SEM) observation is carried out to detect the deformation and damage of the PoP structure under three-point bending loading. The results indicate that the cracks occur in the die of the top package, then cause the crack deflection and bridging in the die attaching layer. Furthermore, the mechanical principles are used to analyse the cracking process of the PoP structure based on the multi-layer laminating hypothesis and the theoretical analysis results are found to be in good agreement with the experimental results. © 2012 Chinese Physical Society and IOP Publishing Ltd.

Long H.,City University of Hong Kong | Wang L.,City University of Hong Kong | Zhang Z.,City University of Hong Kong | Song Z.,Nanjing University | Xu J.,China Longyuan Power Group
IEEE Transactions on Industrial Electronics | Year: 2015

This paper investigates the wind turbine power generation performance monitoring based on supervisory control and data acquisition (SCADA) data. The proposed approach identifies turbines with weakened power generation performance through assessing the wind power curve profiles. Profiles that statistically summarize the curvatures and shapes of a wind power curve over consecutive time intervals are constructed by fitting power curve models into SCADA data sets with a least square method. To monitor the variations of wind power curve profiles over time, multivariate and residual approaches are introduced and applied. Two blind industrial studies are conducted to validate the effectiveness of the proposed monitoring approach, and the results demonstrate high accuracy in detecting the abnormal power curve profiles of wind turbines and their associated time intervals. © 2015 IEEE.

Yong Z.,China Longyuan Power Group | Wei D.,Beijing Longyuan wind power engineering consultation company
European Wind Energy Conference and Exhibition, EWEC 2013 | Year: 2013

With the emergence of grid connection issue and wind power production curtailment,wind power storage is drawing more attentions. The conventional energy storage like battery cannot be applied commercially due to high cost and technological immaturity. Thermal energy storage can be used in wind power application as that electricity from wind power is converted into thermal energy which is then converted into electricity through steam turbine generator. To increase efficiency, combined heat and power generation is used in this application, which is more valuable in the areas as Northeast China and Inner Mongolia. These places are feathered by high wind speed, high heat demands and severe wind power output curtailment.

Liu X.,North China University of Technology | Ma S.,China Longyuan Power Group
2015 IEEE Energy Conversion Congress and Exposition, ECCE 2015 | Year: 2015

In the DC power systems of More Electric Aircraft, the closed-loop controlled electrical motor drives and power electronic converters can be generally regarded as constant power loads (CPLs), and usually lead to negative impedance-related instability. Depending on Brayton-Moser's mixed potential theory, this paper adopts R parallel damping filters to stabilize the CPLs systems, and derives large signal stability criteria. The simple criteria utilize the dynamic negative impedance of the CPLs to place quantitative constraints on the filter parameters, and provide important design guidelines during the filter determination. Comparisons demonstrate the stability criterion for the CPLs with a single-stage LC filter can be regarded as a special case of the proposed criteria. The region of asymptotic stability (RAS) around the stable equilibrium point is obtained, and it indicates the criteria can guarantee the system stability during large disturbances. The experimental results also confirm the validity of the proposed stabilization method. © 2015 IEEE.

Song B.,University of Science and Technology Beijing | Yi Y.,University of Science and Technology Beijing | Wu J.C.,China Longyuan Power Group
International Efforts in Lifeline Earthquake Engineering - Proceedings of the 6th China-Japan-US Trilateral Symposium on Lifeline Earthquake Engineering | Year: 2014

Ensuring the safety of structure is especially important because of the complex environment in service and direction to large-scale. Two types of environment are taken into account, mountain and offshore, and height of structures is respectively 50.0 m and 88.5 m. Bearing behaviors of wind turbine towers in different kinds of load combination are discussed according to Japanese standard in 2010. Then, influence of height, quality and stiffness on displacement and stress are analyzed, and also the dynamic responses of structures in different types and levels of earthquake are studied. It shows that the revised edition of Japanese standard in 2010 is needed to assess the bearing capacity comparing with edition in 2007. The dynamic response of structure is affected by height. When the height increases 177%, the maximum displacement in the top of the tower would increase 231% in 8-degree rare earthquake. Other factors are quality and stiffness and so on. Far-field seismic waves have the largest impact on structures which are high-rise and great flexibility.

Song B.,University of Science and Technology Beijing | Qi F.,University of Science and Technology Beijing | Wu J.,China Longyuan Power Group
Applied Mechanics and Materials | Year: 2013

The process of interaction of sea ice and a pier column structure was studied by using analogue simulation method in the paper, and the dynamic ice force acting on the pier column structure was achieved. Combining with theory analysis, it modified the dynamic ice force model suggested by Croteau. The results show that the loading stiffness suggested by Croteau is too big to use in the dynamic ice force model and the Withalm formula and simulated results are more suitable. The calculation formulas of relative displacement in ice force unloading stage and the continuous ice force in ice force continuous stage also are suggested in the paper. © (2013) Trans Tech Publications, Switzerland.

Wang S.-C.,China Longyuan Power Group | Wu J.-C.,China Longyuan Power Group
Dianli Xitong Baohu yu Kongzhi/Power System Protection and Control | Year: 2014

During several large-scale wind-turbine-generator (WTG) dropout accidents, part of the WTGS were tripped off because the system voltage exceeded the overvoltage protection value of WTGs. One of the problems exposed in the WTG dropout accidents is that some of the relay protections are not properly set up. In this paper, the principles of overvoltage relay protection of WTGs and capacitor banks are investigated, then a method of calculating the voltage drop on WTG's transformers and power collection lines is given; finally, several principles to set overvoltage protection of WTGs and capacitor banks are proposed.

Wang L.,City University of Hong Kong | Zhang Z.,City University of Hong Kong | Long H.,City University of Hong Kong | Xu J.,China Longyuan Power Group | Liu R.,China Longyuan Power Group
IEEE Transactions on Industrial Informatics | Year: 2016

The feasibility of monitoring the health of wind turbine (WT) gearboxes based on the lubricant pressure data in the Supervisory Control and Data Acquisition (SCADA) system is investigated in this paper. A deep neural network (DNN) based framework is developed to monitor conditions of WT gearboxes and identify their impending failures. Six data-mining algorithms, the k nearest neighbors (kNN), least absolute shrinkage and selection operator (Lasso), ridge regression (Ridge), support vector machines (SVM), shallow neural network (NN), as well as deep neural network (DNN), are applied to model the lubricant pressure. A comparative analysis of developed data-driven models is conducted and the DNN model is the most accurate. To prevent the overfitting of the DNN model, a dropout algorithm is applied into the DNN training process. Computational results show that the prediction error will shift before the occurrences of gearbox failures. An exponentially weighted moving average (EWMA) control chart is deployed to derive criteria for detecting the shifts. The effectiveness of the proposed monitoring approach is demonstrated by examining real cases from wind farms in China and benchmarked against the gearbox monitoring based on the oil temperature data. © 2016 IEEE.

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